This invention relates to electrical connectors and, more particularly, to an assembly for providing interconnections between an integrated circuit module and a printed circuit board.
In recent years, a so-called single in line memory module (SIMM) has become increasingly popular. Such a module, or board, is used primarily to carry interconnection support for a series of memory chips and its dimensions are typically about 1/16" thick, 4" in length, and 1/2" or more in width. Typically, a plurality of these modules are supported on, and electrically connected to, a single relatively large printed circuit board. In this configuration, the modules are known as "daughter boards" and the large printed circuit board is referred to as a "mother board". Contact pads are typically positioned on both surfaces of the daughter board, along one of the long edges, with each contact pad being shorted to the pad just opposite it on the other surface, permitting typical SIMM mating connectors mounted on the mother board to use a contact member which simultaneously applies normal forces to both sides of the daughter board, thereby making electrical contact to both of the shorted contact pads. Such a connector is disclosed, for example, in U.S. Pat. No. 4,737,120.
A number of problems have been encountered with presently available SIMM connectors, including warping of the daughter board, difficulty of insertion and removal of the daughter board, and difficulty of withstanding vibration without producing fretting corrosion. Accordingly, it is an object of this invention to provide a connector assembly which is not susceptible to these problems.
Recently, new modules have been introduced having increased memory capacity and which in fact may contain thereon a complete computer of the IBM XT class. Such a module may require electrically unique (separate) contact pads on both surfaces. It is therefore another object of this invention to provide a connector assembly capable of establishing separate connections to contact pads on both sides of a module.
A module, or daughter board, as described above may contain as many as 100 contact pads per side, for a total of up to 200 contact pads. The insertion of such boards into mating connectors requires a substantial insertion force. It is therefore a further object of this invention to provide a connector assembly of the so-called zero insertion force type. The term "zero insertion force" is in actuality a misnomer, since force must be applied at some time. However, the force is not applied directly to the module but rather through an intermediate member.
From past experience, it has been found that the industry does not maintain specified board thickness limits. It is therefore yet another object of this invention to provide a connector assembly capable of accepting boards over a relatively large range of thicknesses.
When installed, the boards described above will be only one of many circuit components. Densely packed electronic components generate substantial amounts of heat which must be removed by an induced air flow. Therefore, the structure comprising the connector assembly must be small, must not obstruct the air flow, and because utilization is in large volumes, must be inexpensive. However, the connector assembly must be capable of withstanding the stresses generated by 200 contacts, each of which applies a 150 gram nominal mating force, while operating in typical environments of 60.degree. C. for a minimum life of 15 years. Accordingly, it is still a further object of this invention to satisfy these requirements by providing a connector assembly of minimal size without requiring the use of expensive materials.